1. Field of the Invention
The present invention relates to processes for removing silicon-containing contaminants from gases. In particular, the present invention relates to processes for removing siloxanes from biogases released from landfills and sewage treatment plants.
2. Discussion of the Background
Landfills and sewage treatment plants contain siloxanes from many sources.
One source is the semiconductor industry, which produces siloxanes as by-products of reactions involving silicon compound gases. Because siloxanes have detrimental effects on semiconductor products, siloxanes are removed from semiconductor process gases by processes such as adsorption onto diatomaceous earth, silica gel, molecular sieves and activated alumina.
The personal care industry uses volatile methyl siloxanes in products such as deodorants, tooth-pastes, skin care preparations, hair conditioners and anti-perspirants.
The cleaning industry finds many applications for siloxanes. In dry cleaning siloxanes are used as a more environmentally friendly solvent than traditional chlorofluorocarbons. In the electronics industry, siloxanes are used to clean circuitry.
Siloxane-containing waste from industrial and domestic sources is discharged into landfill sites and sewage treatment plants, along with a variety of biological organic matter.
The organic matter in the waste decomposes to produce biogas containing various volatile organic compounds, such as methane. The biogas can be used to fuel various combustion engines.
However, the biogas from landfill sites and sewage treatment plants is contaminated with siloxanes. When an engine burns siloxane-contaminated biogas, the siloxane forms precipitates of silicon dioxide. The precipitates are deposited on engine parts such as turbine blades, cylinders, heat exchangers and emission control equipment. The deposits increase the abrasion of engine surfaces, leading to a loss of engine efficiency and premature engine failure. The deposits also poison catalytic converters.
Previous attempts at removing siloxane contaminants from biogas have used adsorbents such as activated charcoal, molecular sieves and silica gel.
Improved techniques for removing siloxanes from biogas are needed.